[jokethrowaway]

I definitely think some people have it easier or harder. I score pretty high in conscientiousness (as in the Big Five, you can test yourself on https://openpsychometrics.org/) and I never had problems working myself off to unhealthy levels.

Because this is what you're looking into doing. If I were you I'd take the signal from your body as a message to stop doing what you're doing, work normal hours, renegotiate your contract to work less for your employer and more for yourself.

If you're still willing to do that and trying to diagnose: Could it be age / family related? I used to work 12-16hrs a day when trying to start my startup. When I went contracting I had to check my hours not to work too much and I was very active on my side projects.

I all changed when I had kids. 5 years of bad sleeping and stress took their toll: I started having health problems and I barely have the energy to work.

The point being: maybe you need to fix some other parts of your life in order to have more energy?

Check your sleep, amount of physical activity, happiness.